Search device for locating buried persons

ABSTRACT

The invention uses four antennae in order to pinpoint the exact position of the transmitter, especially at a close distance. The four antennae form two pairs of antennae placed at a specific angle to each other. The pairs of antennae are respectively comprised of two antennae that are also placed at a specific angle to each other. The pairs of antennae are respectively comprised of two antennae that are also placed at a specific angle to each other. The direction of the field line of the send antenna can be detected by comparing the signal intensities of the antenna pairs. Lateral deviations and forward or rear deviations from the shortest distance point can be recognised by comparing the signal intensities of the corresponding antennae. All signals have the same intensity at this point. Search devices are mainly used by wilderness skiers and those choosing to ski off piete.

PRIOR ART

Search devices for locating buried persons based on transmitter andreception deices using a frequency of 457 kHz, especially for the searchof persons buried by avalanches, have been in use for a longer period oftime (compare patent DE 35 31 726 C1).

These devices suffer from a substantial disadvantage that is caused bythe propagation of the electromagnetic field of their ferrite antenna(compare patent DE 193 10 875 C1) and the fact that the latter signal isonly received by one antenna, i.e., only parallel orientation of theantennae leads to the detection of maximum signal strength given theclosest distance to the transmitter. If a perpendicular orientation ofthe two antennae is given, several maximum signal strengths may occur,which are not in the closest distance to the transmitter. Concerning thesearch for buried persons the problem arises that the latter fact istaken into consideration by the application of time-consuming and highlycomplicated methods, which also require a substantial amount of training(compare “De Alpen” 11/1996—Mitteilungen des Schweizer Alpenclubs).

The invention disclosed in the patent DE 195 10 875 C1 also turns out tobe less practical, because at first, there are three transmitterantennae located perpendicular to each other, which would render such adevice very voluminous and make it impossible to wear it on the body,and second, a proper operation could only be ensured, if transmitter andreceiver are of the same type, which excludes an integration into thealready existing wide-spread types of devices. More recent devices,which make use of two perpendicular antennae (compare patent EP 0 855600 A2), merely improve the first phase of the search for buriedpersons. An accurate localization to the point, however, cannot beachieved.

PROBLEM OF THE INVENTION

The invention is aimed at designing a search device for locating buriedpersons in a manner that allows the searcher to be guided easily anddirectly to the buried person, the latter being also possible with theabove-mentioned wide-spread types of devices.

DESCRIPTION OF THE INVENTION

The invention makes use of two principles:

1. The induced voltage of a coil (=antenna) in a magnetic field is basedon the following physical law:

U=μ₀ N H ΔA

ΔA=A cos α

U: induced voltage

μ₀: induction constant

N: number of turns

H: field strength

A: coil plane perpendicular to the magnetic field

α: angle of the coil plane in relation to the perpendicular axis of themagnetic field

From the latter it can be recognized that the induced voltage isdependent on the angle of the coil in relation to the magnetic field.Consequently, the direction of the magnetic field can be determined ifone uses two coils which are present in a plane and are arranged in acertain angle, and compares the voltages thus induced.

As described in the patent DE 195 10 875 C1, the magnetic field of atransmitter antenna emanates from the latter in an elliptic manner. Ifthe two reception coils, which are arranged in a certain angle withtheir longitudinal axes being each in parallel to the earth's surface,are always orientated in a manner that keeps both induced voltagesequal, and one moves forward in the direction of the median keeping theorientation constant, one arrives at the transmitter coil along theso-called lines of electric flux.

However, the closer one gets to the transmitter coil, the more crucialthe distance between the transmitter and the earth's surface planebecomes, as well as the distance between the earth's surface plane andthe reception device.

2. From the patent DE 35 31 726 C2 it is known that the magnetic fieldstrength is dependent upon the distance to the transmitter coil.

Hence, if two reception coils are arranged in a certain angle to eachother and the longitudinal axis of the transmitter coil is oriented inparallel to the median of the reception coils, the reception coil whichis closer to the transmitter coil will provide the higher inducedvoltage.

Consequently, a single transmitter coil may be localized accuratelyirrespective of its position in relation to the reception coils by meansof two reception coils, which are arranged in a certain angle and twofurther reception coils which are also arranged in a certain angle and,at the same time, are arranged in a certain angle to the first pair ofcoils because only at the shortest distance to the transmitter coil, allfour signals of the reception coils are equal and have the higheststrength.

The transformation of the induced voltages of the reception coils intosignal parameters is accomplished by an electronic circuit which iscommon for the latter purpose. The evaluation may be achieved in ananalog manner, e.g., by means of several moving coil measuring deviceswith one of the latter indicating the tendency of the direction of themagnetic field by adding the signal strengths of the antennae 1(1) and2(2) and indicating a left or right deflection depending on the negativeor positive polarity sign, respectively, or adding the signal strengthsof the antennae 1(1) and 3(3) and subsequently adding the latter to thesum of the antennae 2(2) and 4(4) and indicating a left or rightdeflection depending on the negative or positive polarity sign.

A further moving coil measuring device may be used in order toaccomplish the indication of a lateral deviation within the short rangeby comparing the sums of the signals 1 and 4, as well as of the signals2 and 3. By means of a third moving coil measuring device, the positionof the buried person before or behind the searcher may be determined bycomparing the sums of the signals 1 and 2, as well as of the signals 3and 4.

However, it is much more convenient to convert the signals into digitaldata and subsequent calculation with a microprocessor. Then, theindication device may be a light emitting diode (LED) or a liquidcrystal display.

In both cases, the signal is additionally rendered acoustically, i.e.,with increasing loudness at increasing signal strengths in order toemphasize the approximation of the searcher to the buried person. Doingso, the amplification may be changed in a way that the change inloudness can be perceived more easily.

To be able to use the device as a transmitter, the reception coil isswitched as transmitter coil which subsequently is able to broadcastsignals of the standardized frequency of 457 kHz.

DESCRIPTION OF THE DRAWING

The included drawing shows a possible array of the four antennae, withthe antennae 1(1) and 3(3) forming a pair of antennae as mentioned inthe description, and the antennae 2(2) and 4(4) forming a pair as well.

What is claimed is:
 1. A portable transmitter-receiver device forsearching for and locating of persons buried by avalanches, said devicecomprising: four antennae having main directions for transmission andreception, orientations of said main directions of said antennae beingarranged in a plane, orientations of main direction of a first antennaand a second antenna of said four antennae being arranged transverselywith respect to each other, orientations of main directions of a thirdantenna and a fourth antenna of said four antennae are arrangedtransversely with respect to each other, and orientations of maindirections of said second antenna and said third antenna being arrangedtransversely with respect to each other; a switch for switching saiddevice between a transmission mode and a reception mode, wherein allsaid four antennae are operated as receiving antennae in said receptionmode; and a comparison circuitry wherein said comparison circuitry isadapted to selectively compare a received signal strength of one of saidfour antennae with a received signal strength of each other of said fourantennae in said reception mode.
 2. The device according to claim 1,wherein one antenna is operated as a transmission antenna in saidtransmission mode.
 3. The device according to claim 1, wherein at leastone of said antennae is a helical antenna.